Intensive interest in forming polymer nano-composite optical materials with a high refractive index has developed in recent years as potential applications for such materials in lenses, filters, reflectors, optical waveguides, optical adhesives, and anti-reflection films, have emerged. Incorporating inorganic domains into a polymer matrix is an effective way to fabricate high refractive index composite materials. The refractive index of such composites varies linearly with the volume fraction of inorganic additive. However, typically the size of the inorganic domains must be below one tenth of the wavelength of visible light (400-800 nm) in order to avoid Rayleigh scattering and obtain transparent polymer composites. Controlling the size of inorganic domains by effective dispersion in the nanometer regime therefore is a consideration in developing these materials.
Lead sulfide (PbS) nanoparticles have a high refractive index and can be introduced into a polymer matrix to create high refractive index nanocomposites. For example, PbS nanoparticles have been introduced into poly(ethylene oxide) or gelatin to produce nanocomposites with high refractive indices. However, the polymer matrices used in these studies were water-soluble polymers and the particle-matrix interactions were weak. So the application of such composites is limited in many cases where materials with water insolubility, good thermal stability, and more robust mechanical properties are needed, in addition to optical clarity. Thus, there remains a need in the art to provide nanoparticle materials that are capable of being incorporated in water-insoluble polymer matrices.